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Activation and reconstruction of the spinal cord circuitry is important for improving motor function following spinal cord injury. We conducted a case series study to investigate motor function improvement in 14 patients with chronic spinal cord injury treated with 4 weeks of unilateral (right only) cortical intermittent theta burst stimulation combined with bilateral magnetic stimulation of L3–L4 nerve roots, five times a week. Bilateral resting motor evoked potential amplitude was increased, central motor conduction time on the side receiving cortical stimulation was significantly decreased, and lower extremity motor score, Berg balance score, spinal cord independence measure-III score, and 10 m-walking speed were all increased after treatment. Right resting motor evoked potential amplitude was positively correlated with lower extremity motor score after 4 weeks of treatment. These findings suggest that cortical intermittent theta burst stimulation combined with precise root stimulation can improve nerve conduction of the corticospinal tract and lower limb motor function recovery in patients with chronic spinal cord injury.

Following a spinal cord injury, there are usually a number of neural pathways that remain intact in the spinal cord. These residual nerve fibers are important, as they could be used to reconstruct the neural circuits that enable motor function. Our group previously designed a novel magnetic stimulation protocol, targeting the motor cortex and the spinal nerve roots, that led to significant improvements in locomotor function in patients with a chronic incomplete spinal cord injury. Here, we investigated how nerve root magnetic stimulation contributes to improved locomotor function using a rat model of spinal cord injury. Rats underwent surgery to clamp the spinal cord at T10; three days later, the rats were treated with repetitive magnetic stimulation (5 Hz, 25 pulses/train, 20 pulse trains) targeting the nerve roots at the L5–L6 vertebrae. The treatment was repeated five times a week over a period of three weeks. We found that the nerve root magnetic stimulation improved the locomotor function and enhanced nerve conduction in the injured spinal cord. In addition, the nerve root magnetic stimulation promoted the recovery of synaptic ultrastructure in the sensorimotor cortex. Overall, the results suggest that nerve root magnetic stimulation may be an effective, noninvasive method for mobilizing the residual spinal cord pathways to promote the recovery of locomotor function.

[INLINE:1] Classic paired associative stimulation can improve synaptic plasticity, as demonstrated by animal experiments and human clinical trials in spinal cord injury patients. Paired associative magnetic stimulation (dual-target peripheral and central magnetic stimulation) has been shown to promote neurologic recovery after stroke. However, it remains unclear whether paired associative magnetic stimulation can promote recovery of lower limb motor dysfunction after spinal cord injury. We hypothesize that the current caused by central and peripheral magnetic stimulation will converge at the synapse, which will promote synapse function and improve the motor function of the relevant muscles. Therefore, this study aimed to examine the effects of paired associative magnetic stimulation on neural circuit activation by measuring changes in motor evoked and somatosensory evoked potentials, motor and sensory function of the lower limbs, functional health and activities of daily living, and depression in patients with spinal cord injury. We will recruit 110 thoracic spinal trauma patients treated in the Department of Spinal Cord Injury, China Rehabilitation Hospital and randomly assign them to experimental and control groups in a 1:1 ratio. The trial group (n = 55) will be treated with paired associative magnetic stimulation and conventional rehabilitation treatment. The control group (n = 55) will be treated with sham stimulation and conventional rehabilitation treatment. Outcomes will be measured at four time points: baseline and 4, 12, and 24 weeks after the start of intervention (active or sham paired associative magnetic stimulation). The primary outcome measure of this trial is change in lower limb American Spinal Injury Association Impairment Scale motor function score from baseline to last follow-up. Secondary outcome measures include changes in lower limb American Spinal Injury Association sensory function score, motor evoked potentials, sensory evoked potentials, modified Ashworth scale score, Maslach Burnout Inventory score, and Hamilton Depression Scale score over time. Motor evoked potential latency reflects corticospinal tract transmission time, while amplitude reflects recruitment ability; both measures can help elucidate the mechanism underlying the effect of paired associative magnetic stimulation on synaptic efficiency. Adverse events will be recorded. Findings from this trial will help to indicate whether paired associative magnetic stimulation (1) promotes recovery of lower limb sensory and motor function, reduces spasticity, and improves quality of life; (2) promotes neurologic recovery by increasing excitability of spinal cord motor neurons and stimulating synaptic plasticity; and (3) improves rehabilitation outcome in patients with spinal cord injury. Recruitment for this trial began in April 2021 and is currently ongoing. It was approved by the Ethics Committee of Yangzhi Affiliated Rehabilitation Hospital of Tongji University, China (approval No. YZ2020-018) on May 18, 2020. The study protocol was registered in the Chinese Clinical Trial Registry (registration number: ChiCTR2100044794) on March 27, 2021 (protocol version 1.0). This trial will be completed in April 2022.

Spinal cord injury is linked to the interruption of neural pathways, which results in irreversible neural dysfunction. Neural repair and neuroregeneration are critical goals and issues for rehabilitation in spinal cord injury, which require neural stem cell repair and multimodal neuromodulation techniques involving personalized rehabilitation strategies. Besides the involvement of endogenous stem cells in neurogenesis and neural repair, exogenous neural stem cell transplantation is an emerging effective method for repairing and replacing damaged tissues in central nervous system diseases. However, to ensure that endogenous or exogenous neural stem cells truly participate in neural repair following spinal cord injury, appropriate interventional measures (e.g., neuromodulation) should be adopted. Neuromodulation techniques, such as noninvasive magnetic stimulation and electrical stimulation, have been safely applied in many neuropsychiatric diseases. There is increasing evidence to suggest that neuromagnetic/electrical modulation promotes neuroregeneration and neural repair by affecting signaling in the nervous system; namely, by exciting, inhibiting, or regulating neuronal and neural network activities to improve motor function and motor learning following spinal cord injury. Several studies have indicated that fine motor skill rehabilitation training makes use of residual nerve fibers for collateral growth, encourages the formation of new synaptic connections to promote neural plasticity, and improves motor function recovery in patients with spinal cord injury. With the development of biomaterial technology and biomechanical engineering, several emerging treatments have been developed, such as robots, brain-computer interfaces, and nanomaterials. These treatments have the potential to help millions of patients suffering from motor dysfunction caused by spinal cord injury. However, large-scale clinical trials need to be conducted to validate their efficacy. This review evaluated the efficacy of neural stem cells and magnetic or electrical stimulation combined with rehabilitation training and intelligent therapies for spinal cord injury according to existing evidence, to build up a multimodal treatment strategy of spinal cord injury to enhance nerve repair and regeneration.

Paired associative stimulation has been used in stroke patients as an innovative recovery treatment. However, the mechanisms underlying the therapeutic effectiveness of paired associative stimulation on neurological function remain unclear. In this study, rats were randomly divided into middle cerebral occlusion model (MCAO) and paired associated magnetic stimulation (PAMS) groups. The MCAO rat model was produced by middle cerebral artery embolization. The PAMS group received PAMS on days 3 to 20 post MCAO. The MCAO group received sham stimulation, three times every week. Within 18 days after ischemia, rats were subjected to behavioral experiments—the foot-fault test, the balance beam walking test, and the ladder walking test. Balance ability was improved on days 15 and 17, and the foot-fault rate was less in their affected limb on day 15 in the PAMS group compared with the MCAO group. Western blot assay showed that the expression levels of brain derived neurotrophic factor, glutamate receptor 2/3, postsynaptic density protein 95 and synapsin-1 were significantly increased in the PAMS group compared with the MCAO group in the ipsilateral sensorimotor cortex on day 21. Resting-state functional magnetic resonance imaging revealed that regional brain activities in the sensorimotor cortex were increased in the ipsilateral hemisphere, but decreased in the contralateral hemisphere on day 20. By finite element simulation, the electric field distribution showed a higher intensity, of approximately 0.4 A/m2, in the ischemic cortex compared with the contralateral cortex in the template. Together, our findings show that PAMS upregulates neuroplasticity-related proteins, increases regional brain activity, and promotes functional recovery in the affected sensorimotor cortex in the rat MCAO model. The experiments were approved by the Institutional Animal Care and Use Committee of Fudan University, China (approval No. 201802173S) on March 3, 2018.